Each electric household and professional appliance (hereinafter, appliance, for the sake of conciseness) typically comprises an inner compartment accommodating a rotating drum accessible by a user for loading items (e.g., laundry or dishware) to be treated (e.g., washed and/or dried) and unloading the items after the intended treatment has been accomplished, as well as electric/electro-mechanical components (e.g., electric motors, electric heating resistors) for accomplishing the intended treatment.
As known, such components, coupled between line and neutral potentials of an AC electric power supply, may be affected by phenomena of dispersion of electric power towards ground.
Considering for example insulation failure arising in electric motors (e.g., due to usage wear, overheating, contaminants and/or mechanical stress), undesired electric power (e.g., electric current) may leak towards ground (leakage current).
The leakage current, apart from increasing power consumption, may pose safety hazards. Indeed, while leaking towards ground, the leakage current may also flow through appliance portions that are intended to be non-conductive (often, easily accessible by a user) under normal conditions.
The dispersion of electric power towards ground is to be avoided, since in case the AC distribution network in the user premises where the electric appliance is installed is properly protected, the protection devices intervene and cause the de-energization of all or at least sections of the user premises; even worse, when no proper protection exists, the risk of electric shock for the user is very high.
Most of solutions known in the art are based on leakage current monitoring. As soon as the monitored leakage current has risen a critical value, an alert condition is signaled (possibly, by displaying a proper error code), and the electric appliance operation aborted.
For example, JP2006177973 discloses a monitoring based on sensing a common mode leakage current flowing in a ground wire cable of a motor controller circuit, generating an average leakage current signal from the sensed common mode leakage current, converting the average leakage current into a first PWM signal, generating pulse signals at the rising and falling edges of the first PWM signal, transposing the rising edge and falling edge of the pulse signals to a voltage referenced to ground, and reconstructing (from the pulse signals) a second PWM signal whose duty cycle varies according to the magnitude of the common mode leakage current.